Method of insulating electric cable joints



Jan. 2, 1968 P. D. GILBERT 3,361,605

METHOD OF INSULATING ELECTRIC CABLE JOINTS Filed April 21, 1964 UnitedStates Patent 3,361,605 METHOD OF INSULATING ELECTRIC CABLE JOINTS PeterDerek Gilbert, Chandlers Ford, England, assignor to Pirelli GeneralCable Works Limited, London, England, a British company Filed Apr. 21,1964, Ser. No. 361,469 11 Claims. (Cl. 156-48) ABSTRACT OF THEDISCLOSURE The invention relates to electric cable joints and inparticular, to the application of insulating material thereto, toreplace the original insulation of the cables after the conductors havebeen jointed together.

Many techniques of doing this are available and the method employed inany particular case will be governed in general by the nature of theinsulating and sheathing materials in the cables themselves. Theextensive use nowadays of synthetic resins, for example polyvinylchloride, polyethylene, for insulation and sheathing purposes has causedthe development of new methods of jointing employing tapes and castingresins of various compositions. Some methods make use of special mouldsand pressure injecting devices for applying the casting resin, but itwill be appreciated that different moulds are necessary to deal with themany different sizes of cable. The casting resins must have asufficiently low viscosity to completely permeate the spaces within thejoint before setting. These techniques can therefore be wasteful inmaterial, as the injected resin will tend to migrate along the cablefrom each side of the joint.

The main object of the present invention is therefore to provide animproved technique for applying synthetic resin insulation to anelectric cable joint.

Accordingly, the invention provides a method of applying insulation toan electric cable joint comprising the steps of forming an envelope offlexible sheet material around the joint, charging the envelope with athixotropic resin mix containing a suitable hardener, and manipulatingthe envelope to apply pressure to the resin, thereby causing the resinto flow throughout the joint. The invention thus employs a resin inthixotropic form, that is, a form in which it will flow only under theapplication of pressure, in conjunction with a pressurising means formedin situ. To allow the invention to be readily understood and carriedinto effect, a method in accordance with the invention is describedbelow with reference to the accompanying drawing, in which FIG- URES 1to 8 are perspective views of successive stages in the application ofsynthetic resin insulation to an electric cable joint.

The conductors of two cables 1, 2 shown in the drawings are firstjointed by methods well known in the 8.11;. The jointed conductors arethen wrapped with either a dry or resin-impregnated tape 3 of a meshconstruction as described, for example, in our earlier United Statespatent application, Ser. No. 257,686, now US. Patent No. 3,203,544. Thejoint is then in the condition shown in FIGURE 1. A sheet 4 syntheticresin material, of generally rectangular form, is then bent round thiswrapped 3,361,605 Patented Jan. 2, 1968 core, in a way which will beclear from FIGURE 2. The top edges 5 and 6 of the sheet are next broughttogether as shown in FIGURE 3.

In the next following steps, illustrated in FIGURE 4, side edges of thesheet 5 are folded in together at an angle on lines as at 7, and creasedas at 8; then the side portions round the cables 1, 2 are taped to thecable sheathing with lengths of a suitable self-adhesive synthetic resininsulating tape 9, so as to form an envelope around the cable. Theenvelope is now opened at the top (FIGURE 5) to form a mouth 10 by whichit is filled with a thixotropic epoxy resin mix containing a suitablehardener. The top edges of the envelope are subsequently folded overtogether and creased, thereby forming a closed bag containing the resin.By rolling the top edges of the envelope towards the jointed cables, asindicated in FIGURE 6, pressure is applied to the resin mix, therebyforcing it to flow into the interstices and the insulation of the joint.This stage of the process can be completed and pressure also applied bywrapping the rolled edge 11 and any portion of the envelope stillupstanding, around the joint, so that this appears as in FIGURE 7.

On completion of the pressurising operation, pressure is released, andpressure-stabilisation taking place, the thixotropic resin will hardenand set. The joint to which insulation is thus applied is finallycompleted by a final overall wrapping 13 of suitable self-adhesivesynthetic resin insulating tape, shown applied in FIGURE 8.

The sheet 4 can be a synthetic resin layer laminated with a metal foil,the latter being positioned on the inner side of the sheet as foldedaround the joint. The use of such a laminate will ensure amoisture-proof barrier around the joint and Will also provide anelectric screen.

The resin can, but need not, be of the same chemical nature as thatforming the original insulation of the cable. For example, if they aredifferent and the jointed cables comprise conductors insulated withpolyvinyl chloride, the applied thixotropic resin can be of the epoxytype.

A suitable formulation for the thixotropic resin mix is butyl phthalate)Filler DT 075 (finely dispersed silica) 8 Hardener HY 951(triethylene-tetramine) 10 From the foregoing it will be appreciatedthat the invention provides a simple method of insulating an electriccable joint requiring no pressure injection or special tooling.

As preformed moulds are not required, the invention is applicable tojoints of any siZe or form. Complete impregnation of the joint isassured and loss of resin is kept to a minimum.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. A method of insulating an electric cable joint, comprising the stepsof forming an envelope around the joint by bending a sheet of flexiblematerial around it so as to leave the end edges projecting beyond thecable, folding together adjacent side edges extending between the saidend edges and the cable on both sides so as to seal those side edges,separating the end edges to form a mouth, charging a thixotropic resinthrough the said mouth into the envelope, sealing the mouth by foldingover the end edges and manipulating the sealed envelope to applypressure to the resin the-reby causing the resin to flow around thejoint.

2. A method according to claim 1 in which the manipulation of the.envelope includes folding the end edges over one another to apply thepressure to cause the resin to flow.

3. A method according to claim 2 in which after folding over the endedges any remaining extending portion of the envelope is wrapped aroundthat portion already extending around the joint.

4. A method according to claim 1 in which the side edges of the envelopesheet are, in addition to being folded together, sealed around thecable.

5. A method according to claim 4 in which the side edges of the envelopeare sealed around the cable by means of a Wrapping of self-adhesivesynthetic resin insulating tape.

6. A method according to claim 1 including an initial step of wrappingthe joint with a tape of mesh construction.

7. A method according to claim 6 in which the tape is resin-impregnated.

8. A method as claimed in claim 1 and further comprising applyingwrapping of a self-adhesive synthetic resin insulating tape over theenvelope.

9. A method as claimed in claim 1 wherein the flexible material is alaminate comprising a layer of synthetic resin material and a metalfoil, the foil being at the inside of the envelope.

10. A method as claimed in claim 1 wherein the thixotropic resin is ofthe same chemical nature as the original insulation of the jointedcables.

11. A method as claimed in claim 1 wherein the cables compriseconductors insulated with polyvinyl chloride and the thixotropic resinis an epoxy resin.

References Cited UNITED STATES PATENTS 1/1961 Bollmeier et al 15648 X2/1966 Black 17476 X

